Working his living room like a pumped-up lawyer trying to sway a skeptical jury, J.D. Moss, 17, rattled off the reasons his parents should let him host something he called a "coed sleepover party."

"It's the newest thing," J.D. said, explaining how 20 of his closest friends--male and female--would spend the night playing Ping-Pong, talking and watching movies in the basement until the sun rose.

J.D. tried using parental logic. "It's too dangerous for us to be out late at night with all the drunk drivers. Better that we are home," he told his parents. "It's better than us lying about where we are and renting some sleazy motel room."

His father relented, saying his son's arguments rang true. And since making that speech, J.D. has hosted not just one but two coed sleepovers, the second one last month after he and classmates at Fairfax's Thomas Jefferson High School attended the homecoming dance.

Forget the old slumber parties where teenage girls talked about the boys they had crushes on. These days, those boys are sometimes sleeping in the same room.

Parties like the ones held at J.D. Moss's home in Great Falls have soared in popularity in the past two years, according to parents and educators at several Washington area high schools.

"It's something that is their generation's spin on the sleepover, and they are very big now," said Errol Krass, whose daughter, Laura, 17, a senior at Magruder High School in Montgomery County, has attended coed sleepovers since she was 15. "Parents are always discussing it, worrying about it. It's a big deal."

Debby Innerfield does not let her 16-year-old daughter, Cait, a junior at Montgomery's Sherwood High School, attend such parties. But the fact that so many other teenagers are allowed to go makes it harder to say no, Innerfield said. "Everyone talks about these, and I know the kids hold a lot of them," she said.

Although boyfriends and girlfriends sometimes attend together, many of the teenagers at the all-night parties are not part of a couple. In that respect, the parties are a variation on group dating, where teenagers hang out together but often don't pair off. Some parents say the parties became more common a couple of years ago after school administrators in several districts asked hotels to stop providing rooms to students after big high school events.

"Kids always used to rent hotel rooms," said Joan Graham, a journalism teacher at Sherwood who hears about the sleepover parties frequently. "I guess with these parties, parents think, 'Well, they are at least under my roof.' "

But while some parents find comfort in the coed sleepovers, others are appalled at the idea.

"It's a horrible trend, and parents need to just say no," said Diane Fenner, who has two sons at Arlington's Yorktown High School. "I think it's a bum deal having them all in the same room like that. I have good friends who disagree and let their kids do it. But I think these kids are getting one over on us."

Innerfield said she worries that the sleeping arrangement may lead to sexual promiscuity.

From teenagers, there are conflicting reports about what goes on at the parties. Many say that nothing beyond kissing occurs. Others say boyfriends and girlfriends sometimes go further than that. Some say they occasionally have seen guests take sips from bottles in the liquor cabinet.

Many of those who go to the parties say they obey parental rules carefully because they're grateful just for being allowed to attend.

"It's almost like there is this little voice on their shoulder," said Dan Pisner, who has let his son Elliot, 17, a Sherwood senior, hold several coed sleepovers.

Elliot agreed. "It's true," he said. "You feel happy you are allowed to just be together and have one. We usually spend a lot of time talking and listening to music all night."

Parents have developed techniques for keeping an eye on the teenagers. "You keep the serving bowls for snacks small. That way you have the pretext to go down there and refill," said Edna Breit, whose son Ilan, 17, is a senior at Rockville High School and has hosted several of the parties.

About 12 to 20 students typically come to the Breit house, bringing sleeping bags. They take a dip in the hot tub--with bathing suits on--and watch movies and talk, Edna Breit said.

"I just feel it's definitely better than going to hotels, and this way you know all the kids who are coming over, you know who they are with," she said. "It's not as random."

Joel Moss said he runs a "tight ship," checking off everyone's name as they arrive and then locking the house so that no one can leave and then return. He also warned J.D. that he would lose his car if anyone was caught using illegal substances.

"There are very clear rules," Moss said. "And they all sleep in one big room in the basement, so I doubt they're exhibitionists and are doing anything sexual in front of each other. Plus, I do look in on them."

Kathy Szymanski, whose daughter, Jessica, is a junior at George Mason High School in Falls Church, said she finds out about the person hosting a sleepover before allowing her daughter to go.

But many educators are skeptical. "I am a little leery of these," said Tim Evans, a social studies teacher and co-adviser to the senior class at Woodson High School in Fairfax. "It's sort of a cop-out to say, 'Well, at least they aren't in hotels.' They shouldn't be in hotels anyway. It's this slippery slope. It's like saying, 'We know you are going to drink so you might as well do it in our house.' "

Ray Anderson, principal of H.B. Woodlawn High in Arlington, said the parties are a bad idea unless the parents who host them are willing to stay up all night.

"The parents might be upstairs in their bedroom, conked out, and there might be wild behavior down below," Anderson said. "If the kids are going to be up all night, then the parents have to be up all night."

Many parents said they try to stay up until about 2 a.m. and then make other checks if they wake up during the night. But ultimately, several parents said, they have to trust their teenagers.

At Katie Orr's house in Olney, 10 students from Sherwood High and Magruder High arrived on a recent weekend carrying sleeping bags and snacks. They sprawled out in the living room, munching on potato chips and apples. They watched "Gossip," a movie about the spreading of rumors in school.

There was giggling and talking, but nothing that would cause any rumors on Monday, the students said later.

Laura Krass, who went to the Orrs' party, said her father was reluctant to let her go to the sleepovers but agreed when she explained that it would be like any other night of hanging out with her friends. The only difference, she told him, was that this night would stretch until dawn.

"It's their custom now," said Errol Krass. "Sometimes you can take the moral high ground and say no. But at some point, you have to have some level of trust."